From the Guidelines
Central hypothyroidism is a condition where the thyroid gland produces insufficient thyroid hormones due to inadequate stimulation by the pituitary gland or hypothalamus, characterized by low TSH with a low FT4, as noted in the 2021 ASCO guideline update 1. This condition occurs when the pituitary fails to produce enough thyroid-stimulating hormone (TSH) or when the hypothalamus doesn't release enough thyrotropin-releasing hormone (TRH). Some common causes include:
- Pituitary tumors
- Radiation therapy to the brain
- Surgery affecting the pituitary
- Head trauma
- Certain genetic disorders Symptoms of central hypothyroidism mirror those of primary hypothyroidism, including:
- Fatigue
- Cold intolerance
- Weight gain
- Dry skin
- Constipation
- Mental sluggishness Diagnosis requires blood tests showing low free T4 levels with inappropriately normal or low TSH levels, as outlined in the management of immune-related adverse events in patients treated with immune checkpoint inhibitor therapy 1. Treatment involves levothyroxine replacement therapy, with dosage adjustments based on free T4 levels rather than TSH, and regular monitoring of free T4 levels every 6-8 weeks during dose adjustment and then annually is essential for proper management, as indicated by the guideline 1. In cases of uncertainty about whether primary or central hypothyroidism is present, hydrocortisone should be given before thyroid hormone is initiated, especially in severe symptoms or life-threatening consequences 1.
From the Research
Definition and Causes of Central Hypothyroidism
- Central hypothyroidism is a rare condition characterized by insufficient production of thyroid hormones by the thyroid gland caused by defects in TSH secretion from the pituitary or TRH secretion from the hypothalamus 2.
- It is defined as hypothyroidism due to insufficient stimulation by thyroid stimulating hormone (TSH) of an otherwise normal thyroid gland 3.
- The etiology of central hypothyroidism includes genetic and acquired causes, mainly associated with tumors in the hypothalamic-pituitary region or treatments such as surgery and radiotherapy 2.
Clinical Features and Diagnosis
- Fatigue and peripheral edema are the most specific clinical features of central hypothyroidism 3.
- Diagnosis is established by the presence of normal to low-normal TSH on the background of low-normal thyroid hormones, confirmed by the thyrotropin releasing hormone stimulation test 3.
- The diagnosis of central hypothyroidism is based on low circulating levels of free T4 in the presence of low to normal TSH concentrations 4.
Treatment and Management
- Levothyroxine treatment is essential for correcting hormonal imbalances and improving quality of life in patients with central hypothyroidism 2, 3, 5.
- Treatment should be tailored according to free or total T4 levels, which should be maintained in the upper half of the normal range for age 6.
- Appropriate doses of levothyroxine for T(4) replacement therapy have not been confirmed, but might need to be higher than presently used empirically in patients with central hypothyroidism and should be adjusted according to age and other hormone deficiencies 5.